1. Field of the Invention
The present invention relates generally to a suspension assembly for speakers. Specifically, this invention teaches a suspension assembly that provides greater stability, including at maximum diaphragm excursions, thus translating into greater volume output, increased frequency range and refined sound reproduction.
2. Background Information
A traditional speaker design is comprised of a diaphragm, a motor assembly, and one or two suspension assemblies. The magnet, voice coil, pole and the structures supporting these components comprise the motor assembly. Sound from a speaker is generated from the application of an electric signal to the voice coil, causing an electric field from the voice coil which crosses magnetic flux from the magnet assembly. This cross product of the electric field with the magnetic field causes axial movement of the voice coil and speaker's diaphragm along an axis orthogonal to the plane of the diaphragm.
A traditional speaker suspension controls and ultimately limits the movement of the diaphragm along the pole. A typical speaker includes two suspensions: one primary and one secondary. The primary suspension couples the outer circumference of the diaphragm to the speaker frame. The secondary suspension, axially spaced behind the primary suspension, couples the voice coil to the speaker frame.
The two suspensions work together to maintain linear movement characteristics, also known as excursion, of the voice coil and diaphragm. Since the diaphragm is connected to the voice coil, the diaphragm's movement generates air pressure and, ultimately, sound. It is important to maintain linear excursion of the diaphragm along the pole in order to minimize instability in diaphragm movement and to allow the rapid movements that generate a wide range of frequencies.
The typical audible frequency range for human ears is between 20 to 20,000 hertz. In order to generate a 20 hertz frequency, a diaphragm has to move 20 times per second. Similarly, to generate a 20,000 frequency, a diaphragm has to move 20,000 times per second.
The sound pressure level of a speaker is determined by the surface area of the diaphragm and by the amount of excursion per vibration. In other words, the more air that is pushed by the diaphragm's movement, the louder the sound generated. To maintain a constant sound pressure level, a speaker diaphragm needs to move 4 times the excursion for every halving of frequency.
A traditional speaker design is constrained by the fact that it is very difficult to produce a single speaker capable of producing the entire range of audible frequency. In order to generate subsonic frequencies near or about 20 hertz, a speaker needs to have a diaphragm large enough to capture and move a lot of air at once to generate the subsonic tones. Accordingly, low frequency speakers tend to be large in size to meet the volumetric requirements and have stiff and heavy diaphragms to prevent buckling under high excursion demands. Such low-frequency speakers are also commonly referred to as woofers.
Woofers, when asked to produce high frequencies, will not be able to move fast enough to generate frequencies anywhere near 20,000 hertz because of the mass, weight, and stiffness of its diaphragm. Accordingly, speakers designed for reproduction of high-frequency sounds, or tweeters, tend to have small diaphragms, low mass and minimal inertia so that it can vibrate at frequencies close to or above audible frequency range.
A typical tweeter or compact speaker has a diaphragm with a diameter between 0.5 to 2 inches and contains very low mass so that it can vibrate at high velocity. However, because a tweeter does not need to have a high excursion to generate audible sound and also has a lesser need for maintaining linearity in movement as a result of the low excursion, most tweeters forego the second suspension. While this typical design is suitable for speaker assemblies which incorporate separate woofers and/or midrange speakers, many speaker assemblies do not have space for a woofer or mid-range speaker. This is the case with the advent of many portable consumer goods, including devices such as ipods, hands-free mobile phones and computer laptops.
In devices with limited space in which compact speakers are used as the main speakers, mid to low frequency response is diminished due to the limited frequency range of a typical compact speaker design and its lack of a secondary suspension. Without a secondary suspension, the diaphragm movement is susceptible to significant wobbling at high excursion. The wobbling can affect the volume output and distort the sound output, thereby limiting the audible range and application of a tweeter.
In order to increase frequency range and reduce wobbling the present invention discloses a secondary wire suspension assembly for compact speakers. The additional wire suspension helps maintain linearity in diaphragm movement and provides greater stability at maximum diaphragm excursion, translating into greater volume output, increased frequency range and finer sound reproduction. The secondary wire suspension can also be used to conduct electricity to the voice coil.
From the preceding descriptions, it is apparent that the devices currently being used have significant disadvantages and/or limitations. Thus, important aspects of the technology used in the field of invention remain amenable to useful refinement.